Serving parts of North West London and the Home Counties.

Advice on Drinking Water Quality

Why does my water look white or milky?

Please do not be alarmed. Air in your water is the most common cause of white or milky water. This sometimes happens if the pressure in the mains has changed. This can happen following a burst or repair, when a fire hydrant nearby has been opened, it may be due to a faulty tap or that your stop tap has been operated.

There is an easy way to prove this is air. You should fill a clear glass with water and watch carefully. You should see that the water will clear from the bottom upwards as the air lifts out of the water. The water should become completely clear with no sediment or discolouration. If the water does become clear, this is definitely aerated water. Air does not affect the quality of your water and will generally clear over time.

The advice above refers to air in your cold water system, if you are noticing cloudiness or air in your hot water but water from your cold kitchen tap is clear, we cannot advise. We suggest that you refer to the instruction manual for your heating system/boiler or contact the manufacturer or a qualified heating engineer.

You may sometimes see a milky film on top of the water. The film is caused by minute traces of calcium carbonate which are normally dissolved in the water but get forced out of solution by the air. You may also notice a slight increase in the chlorine or 'swimming pool' smell which again is because the chlorine is forced out of solution.

The aeration generally clears within one or two hours. If it goes on for longer or you are concerned please contact us and we can advise you further.

Watch our video for advice on dealing with discoloured or aerated water


General information on water hardness

The area that we supply water to is generally 'hard' or 'very hard' water. 

This hardness occurs naturally and does not vary very much over time. After rainwater, which is naturally soft, has fallen on the ground it percolates through the underlying rocks and some of the rocks’ constituent minerals dissolve into it.  Predominantly these minerals are calcium and magnesium and are beneficial to healthy teeth and bones.

There are no standards for hardness in the Water Quality Regulations, neither are there any health based standards for the hardness of drinking water. However, ‘soft’ drinking water (with a calcium carbonate value of 100 mg/l or less) will be more corrosive to internal metal pipework.

Customers in the area of the former Borough of Saffron Walden receive water which is softened by Affinity Water prior to distribution, for which they pay an additional charge on their water supply charges.  This is due to an inherited Order, the Lee Valley Water Order 1963, which the Company honours even though the Borough no longer exists.

Water Hardness


Upon heating hard water produces ‘scale’ and so hot water systems, kettles, electric irons and domestic appliances are particularly prone to ‘scaling up’. It also leaves ‘tide marks’ on basins, sinks, baths and toilets and a scum on the surface of hot drinks, especially tea brewed in the cup with a teabag (due to the air and oil in the tea). Scale and scum is not harmful, but we appreciate you may find it aesthetically unpleasing.

To reduce the build up of scale:

  • In kettles – don’t re-boil any water left in a kettle that has previously been boiled, refill with fresh water from the tap or from a jug kept in the fridge.

  • In hot water and heating systems – adjust the temperature that the water is heated to 60oC or below. This will not only save you money, but also reduce the risk of scalding from the water being too hot.

We do not recommend the use of de-scaling products to remove scale in kettles, but if you wish to make sure you take care to follow the manufacturer's instructions and be aware that in the short term there might actually be an increase in the amount of scale you notice in the water after it has been heated. This is because the scale that comes out of the water has no available scale layer to adhere to anymore.

Should I fit a water softener?

Hard water produces less lather from soap, washing up liquid and washing powders. If you feel you would like the water ‘softened’ you can consider installing a domestic water softener. We are not in a position to offer advice to customers on makes or types of water softener and would recommend customers wishing to install a water softener to contact an approved plumber. You can find details here Approved Plumbers. These plumbers will be able to advise you on the most appropriate type for your circumstances and requirements.

Please remember, if you are considering installing a water softener always keep a separate un-softened mains fed tap for cooking and drinking purposes as most softeners replace the calcium and magnesium with sodium. This can be a particular problem for premature babies and for people who are on a low sodium (low salt) diet. Artificially softened water may also be more aggressive to plumbing causing increased leaching of copper and lead into water as it stands in pipework.


Common problems with water softeners

One common problem associated with domestic softeners is when there is ‘breakthrough’ of resin beads from the softener. The beads, which are usually small, round, light coloured balls can then be drawn through in the cold water supply. In cases such as this you should contact the manufacturer or installer of the unit to rectify the problem.

A similar problem can occur with jug filters. Sometimes the carbon held in the filter body, which look like small, black particles can be forced back through the top of the filter into the top of the jug supply. This gives the impression that there are black bits in the incoming water supply. You can check whether this is happening by filling a glass with water before filling the jug filter – as long as the water is clear before you put it in the jug filter you can be assured that there is nothing wrong with the quality of the incoming supply. Changing the filter will usually rectify this problem.

Water Conditioning Devices


Water conditioning devices are a wide range of products that are designed to reduce the build up of lime-scale deposits on heat-exchange surfaces when hard water is heated. These devices do not soften water. There are many types of these devices on the market e.g magnetic, electrolytic, electronic, with a variety of claimed operating mechanisms. It is generally understood that water conditioners are not completely effective in preventing lime-scale build-up – they reduce scale build-up by modifying the form of the scale produced making it less likely to stick on heat-exchange surfaces. These devices appear to be most beneficial when they are fitted to the water inlets to boilers and other water heating devices. Should you wish to have a unit fitted we would advise you use a reputable manufacturer or dealer – a selection of these can be found on the UK Water Treatment Association website


General information on Tastes & Odours

Water supplies in the UK come from a variety of sources including chalk boreholes, upland reservoirs and lowland rivers. Each of these has its own characteristic taste and explains why you might have noticed differing tastes to drinking water as you move around the country.

Although some people are more sensitive to taste and odour than others, unpleasant tastes and odours in mains water are very rare. However, if you notice a particularly bad taste or odour which means you cannot drink the water, or you notice a taste or odour for the first time, please contact us

All of the following common tastes and odours are applicable only to the mains fed cold water tap. If you are experiencing any of the following from a hot tap or internal storage fed tap then you should contact a plumber.


Watch our video for advice on dealing with tastes or odours from your water supply


Tastes and Odours


To ensure that water arriving at your property is free from harmful bacteria a small amount of chlorine is added at our treatment works, which is maintained throughout our distribution network to provide residual disinfection at your drinking water tap. Therefore, you may be able to smell a trace of chlorine in your cold water supply. Although we aim to keep chlorine levels to a minimum these do vary, not only throughout the day, but also across the year. There are also operational reasons, for example following a burst water main, when you might notice slightly elevated levels of chlorine.

Solution – place a covered jug of water in the fridge for a couple of hours before drinking. This will allow any residual chlorine to dissipate. Ensure that any water not used within 24 hours is discarded and replenished with fresh water.

Chlorine has been used to disinfectant drinking water for over 100 years and at the levels added it is not harmful to health. These levels are routinely monitored at our treatment works, during distribution and at customers’ properties.

Antiseptic/TCP in cold water

Traces of chemicals routinely used in the manufacture of flexible plastic hoses, usually those that supply cold water to dishwashers or washing machines, can interact with chlorine to create an antiseptic or TCP-type taste. When the drinking water tap is turned on a small amount of the water lying in these hoses can be drawn back into the cold supply. This problem usually occurs when the hose is connected directly onto the rising main. To check whether these hoses are causing a taste close the isolating valve for 24 hours and check the taste again.

Solution – either change the hoses for those approved under the WRAS (Water Regulations Advisory Scheme), for example a food quality hose, or change the isolating valve for one fitted with a check valve, also known as a one-way or non-return valve.

This type of taste can also be caused by a having garden hose permanently connected to an outside tap.

Solution – remove the hose from the tap when not in use and check that a double check valve is fitted and functioning properly between the tap and the hose. A qualified plumber will be able to offer advice on this issue.

As with all fixtures and fittings plumbing materials deteriorate over time. Very old washers can begin to disintegrate or become damaged, for example by a worn tap seating, and can change the taste of your water. The most commonly affected areas are the kitchen tap and the stop tap.

Solution – replacing old and worn out washers and or tap seats will help improve the taste.

The consumption of water with this taste, although unpleasant, is not harmful in itself.

Antiseptic/TCP after boiling

Sometimes taste problems can arise after water has been boiled. As a general rule, if your drinking water is satisfactory prior to boiling and you then notice a taste after boiling the cause of the problem is usually the kettle. Boiling water in a saucepan on your hob or stove will help determine if your kettle is the cause of the unusual taste.

Solution – if the kettle is new allow a layer of limescale to build up inside it by boiling and then discarding the water a few times. Only boil the required amount of water each time. Do not re-boil water, rather discard it, rinse the kettle and fill with fresh water. Also try to avoid frequent de-scaling of the kettle.


Elevated levels of metals can be introduced via customers’ internal pipework and can cause a metallic or bitter taste. This is most apparent after water has been standing in pipework for a period of time, for example overnight. It may also be noticed where there are long runs of pipework or in situations where water becomes warm as it passes to a drinking water point.

Solution – if the pipework is new the taste should improve with time as a thin protective layer of limescale will form on the inside of the pipework. Where water heats up during transit you should check the routing of pipework and the proximity of cold and hot water pipes. Affected pipework should be lagged or re-routed as necessary. Flushing the tap to clear any water which has been allowed to stand should also help.


Sometimes a sewage or stagnant type odour can emanate from a sink/plug hole, indicating a possible blockage or build up of waste materials, making the drinking water appear as if it has an odour. Filling a glass with water and smelling it in a different room, away from the kitchen sink, will help to determine whether the odour is genuinely from the water or not. If you think it is the water please contact us immediately.

Solution – if the odour disappears when away from the sink you should try cleaning your sink/plug hole with a normal domestic cleaner. However, if there has been recent work on your service pipe, or you have had a new connection to your property, it could indicate a problem with this work and you should contact us immediately.


A petrol/diesel/oil taste or odour can occur if the ground around a plastic pipe becomes contaminated, for example following leakage from a car’s petrol tank or an onsite heating fuel storage tank, as petrol/diesel/oil can permeate through plastic pipework. If you notice this type of taste or odour, or are aware of a leak or spill of petrol/diesel/oil on or in the vicinity of your property, do not consume your water and contact us immediately. An Affinity Water representative will visit you to assess the situation.